1. Field of the Invention
The present disclosure relates to an image pick-up apparatus.
2. Description of the Related Art
An image pick-up apparatus using a curved imaging surface has been developed. Japanese Patent Laid-Open No. 2005-338341 (Patent Literature 1) discloses an image pick-up apparatus including a ball lens and an image-surface conversion element that is a bundle of optical fibers each having an opening end that faces a curved image surface of the ball lens. Patent Literature 1 also discloses a configuration in which all the optical fibers of the image-surface conversion element are aligned in the longitudinal direction, at the opening ends, with the direction of the center of the ball lens.
US Patent Application Publication No. 2014/0015997 (Patent Literature 2) discloses an image pick-up apparatus including an image sensor curved to be concave with respect to an object side.
With an image-surface conversion element as in Patent Literature 1, an increase in the angle of incidence of an off-axis beam incident on the ball lens relative to its optical axis increases the exit angle of the beam exiting from the image-surface conversion element relative to its optical axis. This causes the beam to enter an image sensor from an oblique direction out of a direction perpendicular to the image sensor. This decreases the photoreceptive sensitivity of the image sensor.
With a curved image sensor as in Patent Literature 2, an image sensor curved in the same shape as that of the imaging surface has a large amount of sag in the periphery of the image sensor, making it difficult to manufacture the image sensor. An image sensor curved to a radius of curvature larger than the radius of curvature of the imaging surface to reduce the amount of sag would disadvantageously decrease the photoreceptive sensitivity of the image sensor, described above.